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Garmin Nuvi 750

I purchased GPS in December 2007 and was recently told that the longitude/latitude coordinates that I had given were not accurate according to the street address I had also given. I need these coordinates to be accurate. I have called Tech Support and they had me reset the unit to reaquire satelites quicker. Tech Suport also said they would send instructions on how to update maps but to date I am still waiting and that was two weeks ago. What can I do about inacurate coordinates as confirmed by another Garmin eTrek unit.

Comments

  • SergZak 340 Points
    What is the unit in question & what kind of accuracy are you looking for? The actual street address will probably never coincide exactly with the actual latitude/longitude coordinates. There is accuracy error with both the GPS and it's positional accuracy (depends on number of satellites seen & locked along with their geometry) and the maps and the way that they are created. The maps don't use lat/long coordinates when it comes to street numbering.

    If you are seeing very bad accuracy as you seem to imply, then maybe it is the fault of the GPS unit, which Garmin can likely replace for you if it is deemed that the unit itself is actually out of spec.

    It also may be that you are simply expecting too much from today's current technology.
  • Tim 1480 Points
    How far off were they? Having a street number 500 meters of from the actual location isn't unheard of.
  • lalalinda 0 Points
    I have the Nuvi 750 model.

    The degrees are accurate. It is the minutes that are off by 10 to 15 and I have not compared the seconds. This happens with both long and lat although the lat minutes are only off by 5-10 as oposed to 10-20.
    This puts me about 40 plus miles off my target which I am hoping would not be acceptable to a company like Garmin.
  • Tim 1480 Points
    When you look at the map does it show you 40 miles off as well? Or does it show you in a reasonable location?
  • I have the Nuvi 750 model.

    The degrees are accurate. It is the minutes that are off by 10 to 15 and I have not compared the seconds. This happens with both long and lat although the lat minutes are only off by 5-10 as oposed to 10-20.
    This puts me about 40 plus miles off my target which I am hoping would not be acceptable to a company like Garmin.
    So I assume you're comparing the Garmin lat/lon with a known lat/lon? If so, how do you know the known lat/lon is correct?

    Also, the lat/lon calculations are based on a "datum" (if I'm using that term correctly), and the most common one is WGS-84. There are other less common datums. I think it's based on assumptions about the shape of the earth, or something like that. Don't quote me on that; this is just from memory because one of my older Garmins had a way to set different datum sets for the lat/lon. Anyway, to make a long story short, are known lat/lons based on WGS-84?
  • lalalinda 0 Points
    The map on the Garmin works fine and gets me to where I need to go and is accurate. It is just the long/lat and I know this as I checked again today with my little Garmin and adain today the long coordinates in minutes were off by 20 and the Lat was off by 10 but the map got me right to the door.
  • BobH 0 Points
    Relative to street address accuracy: It was expalined to me by NavTeq that for many streets, an assumption is made that the street is divided up into 100 addresses. As such, I live on a street with perhaps a dozen homes and although I live at #16. It shows up as #44 on the GPS when using NavTeq maps (City Navigator). With the older Metroguide maps produced by TeleAtlas my address was right on.

    For longer streets, addressing appears to me to be reasonably accurate.

    Overall, City Navigator far more accurately displays the actual location of roads.

    I don't know my actual coordinates, so can't make a judgement as to the accuracy of those numbers given on the GPS.

    Bob
  • The map on the Garmin works fine and gets me to where I need to go and is accurate. It is just the long/lat and I know this as I checked again today with my little Garmin and adain today the long coordinates in minutes were off by 20 and the Lat was off by 10 but the map got me right to the door.
    How did you reach the conclusion that the lat/lon is wrong?
  • lalalinda 0 Points
    Thanks for your questions.

    I use GPS coordinates and give them to someone else for work and when they entered the civic address in Google Earth, it was accurate but when they entered by coordinates, they had me in another area about 40 miles away. I then compared serveral coordinates with the Garmin e-trek and found them to out on the minutes by 20 minutes.

    I cannot trust the coordinates from my Garmin Nuvi 750 at this rate which is not what I expect from the product and the reason I updated by GPS was so that I would have the coordinates to work with.
    I was previously using the Street Pilot 530.

    Any further help/suggestions would be appreciated.
  • Tim 1480 Points
    I can't imagine any circumstance where the coordinates would be 40 miles away from the actual location unless they were entered improperly or were entered using a different format from what they should have been (decimal, degrees, dms, etc).
  • Tabs 0 Points
    Yeah that really sounds like an entry mistake or something - are you sure you got the address correct when you entered it in? Sometimes it'll give you a choice between a West or East or a North or South version of the address, since you don't input directions on the unit, just the street name.

    There's something seriously wrong if it's 40 miles off.

    If I turn my unit on in my house and go to the satellite status or Where am I screens and look at the Lat/Lon, it's extremely accurate when comparing to Google Earth.
  • So you're saying that you have the 750 and e-trek next to each other and they show different coordinates?
  • Tim 1480 Points
    40 miles off certainly sounds like a coordinate format error... Using DMS when you were given decimal degrees or something like that.
  • kwhunter 0 Points
    Call customer service, get an RMA and return the unit.
    Thanks for your questions.

    I use GPS coordinates and give them to someone else for work and when they entered the civic address in Google Earth, it was accurate but when they entered by coordinates, they had me in another area about 40 miles away. I then compared serveral coordinates with the Garmin e-trek and found them to out on the minutes by 20 minutes.

    I cannot trust the coordinates from my Garmin Nuvi 750 at this rate which is not what I expect from the product and the reason I updated by GPS was so that I would have the coordinates to work with.
    I was previously using the Street Pilot 530.

    Any further help/suggestions would be appreciated.
  • raaurora 0 Points
    that is exactly what I was thinking. There are 3 different formats for coordinate entry and the factory default is not the format you get from google or yahoo maps.

    I had to change my default setting so it matched the format used by google and/or yahoo. 40 miles just can't be right.

    but, as a test, if the original poster posted the address, could we all put it into our nuvis and post the coordinates? that would quickly determine if the problem is a default setting.
  • Tim 1480 Points
    that is exactly what I was thinking. There are 3 different formats for coordinate entry and the factory default is not the format you get from google or yahoo maps.
    And that too is why I asked if the device itself shows you reasonable nearby on the map from where you actually are. If it is (as I suspect) then we know it is a coordinates format or transposition error and not a faulty device.
  • lalalinda 0 Points
    Tim-

    Could you please explain what a coordinates or transposition error is.

    I am not sure what you mean on this one.
  • Tim 1480 Points
    Transposition just = typo. But boordinates can be displayed in many different formats. These coordinates all reference the same location for example, but are expressed in different formats.

    45.031591, -70.313176
    45° 1.8955, -70° 18.7906
    45° 1' 53", -70° 18' 47"

    And there are other formats as well.
  • lalalinda 0 Points
    Thanks Tim.

    So when I use my GPS to determine the Long/Lat and it give me

    46° 14".600 N and 70° 07.542 W or whatever when I ask it where I am, should I not expect it to be fairly accurate when it has taken me to the door of the address I entered ?
  • Tim 1480 Points
    So when I use my GPS to determine the Long/Lat and it give me or whatever when I ask it where I am, should I not expect it to be fairly accurate when it has taken me to the door of the address I entered ?
    Yes, IF the format the GPS is set to enter is the same format as the coordinates you have. The coordinates you listed for example are ambiguous. The latitude value you listed for example looks strange. There are no minutes listed and what would appear to be the seconds is listed as a decimal. The longitude value looks good as a Degrees Minutes value.
  • Lalalinda, so you're saying that you have the 750 and e-trek next to each other and they show different coordinates? And you think the e-trek is correct? If so can you tell us the exact numbers each one displays, including the spaces, dots, etc.?
  • lalalinda 0 Points
    I just took both units outside and now that I have heard your descriptions, I see that the two units record coordinates in different formats. However, it still does not account for the discrepency of 40 miles for the Nuvi .

    N46°14.595', W063°07.649' for the Nuvi

    N46.24322°, W063.12736° for the eTrek

    Any information would be helpful. I have reset the Nuvi yet again in hopes that coordinates might get more accurate and it is possible that they are now putting me within 5-10 miiles. It would be nice not to have to wonder where the coordinates would put me on the map every time I record them.
  • Tim 1480 Points
    N46°14.595', W063°07.649' for the Nuvi

    N46.24322°, W063.12736° for the eTrek
    Those two coordinates are in different formats. Once is in Degrees Minutes, and the latter is in Decimal degrees. When compared to each other they are only about 23 feet apart.
  • lalalinda 0 Points
    Interesting. So, from the coordinates that I gave you and if they are only 23 feet apart, could you please use the Navi coordinates and tell me what the civic address is from those coordinates.

    Perhaps the resetting of the Nuvi 750 has accomplished the task of getting back on track. That would certainly be great if it was the case.
  • Tim 1480 Points
    could you please use the Navi coordinates and tell me what the civic address is from those coordinates.
    I'm not certain what you are asking. If you want to know where those coordinates are, they are on Alexander Dr in PEI.
  • Perhaps the resetting of the Nuvi 750 has accomplished the task of getting back on track. That would certainly be great if it was the case.
    ??? The 750 wasn't the problem. You were interpreting the coordinates wrong. You gave us two sets of coordinates, one from the eTrex and one from the Nuvi, and you said that those numbers were 5-10 miles apart. But they weren't. Tim verified that they were 23 feet apart. So what you need to do is go back to Google Earth, or whatever you use to verify that the coordinates are correct, and enter both sets of coordinates. If you're still showing that they're 5-10 miles apart then you still have a problem. And the problem isn't related to the 750, right?
  • lalalinda 0 Points
    Thank you for that. I will certainly ask the person who noted the discrepency to rechek my next set of coordinates to see if the problem still exists or if we have gotten it resolved.

    I know we were doing okay last year with no problem so I will try again and see what happens.

    Thanks for you time on this. I would like to thinkmy device is not the problem.
  • tcris52 0 Points
    I just bought a Nuvi 750 because it allowed me to use the SD card I had for Thailand. However, I found that there is no way to change the datum from the default. This will give error once you get outside the datum coverage area (United Status, I assume).

    I still can't believe that Garmin would release a product that allows you to use their SD cards with this obvious defect.
  • I just bought a Nuvi 750 because it allowed me to use the SD card I had for Thailand. However, I found that there is no way to change the datum from the default. This will give error once you get outside the datum coverage area (United Status, I assume).

    I still can't believe that Garmin would release a product that allows you to use their SD cards with this obvious defect.
    That's a good point. I scanned the Garmin website and couldn't find an answer.

    When Garmin sells a map for a region with a different datum (like Thailand, perhaps), does Garmin convert the map to the default WGS84 datum? Or does Garmin automatically switch to the datum of the new map, i.e., the datum tables (or whatever format they're in) are stored on the SD card? If it does neither, then I'd agree that there is an obvious problem. It's hard to see how Garmin could have overlooked this. Surely they either convert maps or load new datum?
  • I just bought a Nuvi 750 because it allowed me to use the SD card I had for Thailand. However, I found that there is no way to change the datum from the default. This will give error once you get outside the datum coverage area (United Status, I assume).

    I still can't believe that Garmin would release a product that allows you to use their SD cards with this obvious defect.
    BTW, when you load the Thailand SD card does the datum change? I assume you can read the datum type in the system menu, or maybe the diagnostic menu. I don't remember.
  • tcris52 0 Points
    HFB,

    You would think the units now would be smart enough to make the change either based on the card or based on where it knows you are (preferably the latter). However, this does not seem to be the case. I can't find any reference to the datum in the unit info that is called up with the diags.

    I have an email in to support mentioning that I think they blew it and what unit would work.

    BTW. I have a Etrex that I got last time I went there, which is why I bought the SD card for Thailand. It has datum change and it works great. I got the Nuvi because it is easier to use on a motorbike or a car.

    Tony
  • If I understand datum correctly, it seems that you could put the SD card into each Garmin and display the lat/lon for a specific spot in Thailand. If the lat/lon is significantly different, then you're definitely onto something. However it's possible that even if Garmin is using the wrong datum on the Nuvi that it may not matter in Thailand. The two datums may just happen to be very similar.

    Let us know what Garmin says.
  • tcris52 0 Points
    That's an interesting point. At first I thought that the lat/long would be correct anywhere since it's being calculated from the satellites ... that the error would come in from the mapping data itself. Now I may have talked myself out of that.

    I'll see if I can get Garmin to give a good explanation of what happens to map data in different areas of the world.
  • Yeah, apparently the US GPS satellites provide data in WGS84 format. I was surprised that it wasn't lat/lon. But I think that my surprise simply shows that I'm exceeding my knowledge base.
  • tcris52 0 Points
    That make two of us. I'll post a reply if I get anything from Garmin that adds to the discussion.
  • Tim 1480 Points
    Yeah, apparently the US GPS satellites provide data in WGS84 format. I was surprised that it wasn't lat/lon.
    lat/long are simply a set of coordinates. WGS84 describes the type "units" for the coordinates. So think of it like this, in comparison to a more common example.

    Coordinates is a measurement unit... like "length". There are multiple "units" we can use to measure length, such as meters and feet. There are multiple "units" we can measure coordinates in too... like WGS84, NAD27, NAD83.

    So if something is in WGS84 format (or meters) then we have a mesurement of coordinates (or length).
  • lat/long are simply a set of coordinates. WGS84 describes the type "units" for the coordinates. So think of it like this, in comparison to a more common example.

    Coordinates is a measurement unit... like "length". There are multiple "units" we can use to measure length, such as meters and feet. There are multiple "units" we can measure coordinates in too... like WGS84, NAD27, NAD83.

    So if something is in WGS84 format (or meters) then we have a mesurement of coordinates (or length).
    So, if I can use some phrases that I only half understand, the problem with lat/lon is it requires a clear understanding of what shape it is being applied to. The earth isn't a perfect ellipsoid (or whatever the shape is) and therefore datum is used to describe it more accurately. And it does this by applying north/south and east/west length corrections?

    Is that in the ballpark of what you're describing, or did I get it horribly wrong?
  • Tim 1480 Points
    In the ballpark, yes. I wouldn't necessarily say "corrections" in the last sentence... Just rather the different datums describe a different shaped earth. The coordinates for each datum are "correct" for the datum being used, but as we more accurately represent the shape of the earth we create new datums to describe that shape.
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